VII. Perception
• Sensation:
- “raw” material for perception
- started at “entry level”, data driven
“bottom-up processing”
• Perception: “top-down processing”
- concept driven, use preexisting knowledge
to interpret information.
VII. PERCEPTION
• Recall – we are bombarded with possible “energy”
from environment...
• A. To what sensations do we attend?
• In order to perceive something, we must attend or pay
attention to it (consciousness).
Selective Attention:
• Ability to focus awareness on a single stimulus to the
exclusion of other stimuli.
(We focus our awareness on only a limited aspect of
all that we are capable of experiencing.)
B. How do we organize stimuli?
• We tend to organize stimuli into “wholes”.
• Origin: Gestalt Psychology
– “Gestalt”: means “whole” or “form” in German.
• Proposed nervous system is predisposed to
respond to patterns in stimuli according to
certain rules.
• “Whole is different from its parts”
• Example from video – wooden “triangle”
C. FORM PERCEPTION
• One of these basic rules...
• 1. Figure vs. Ground
– To see an image, need to be able to distinguish
between figure and ground.
– Sometimes, they can be reversible.
– But, at one time, we can focus on only one or other.
dging Distance
man
ive
y
C. FORM PERCEPTION
• What stimuli are grouped together?
• 2. Grouping
- We automatically imply order by grouping
things together according to certain rules.
D. DEPTH & DISTANCE PERCEPTION
• How do we perceive depth/distance?
- Image on retina is 2-d.
- Need the brain – uses certain cues.
1. Depth perception:
• a. Binocular Cues:
Cues for perceiving depth that require both eyes.
- Retinas receive slightly different images of world.
- Brain compares those 2 images.
- Retinal Disparity: difference between 2 images.
- Key to judging depth – SHORT DISTANCES.
D. DEPTH OR DISTANCE
PERCEPTION
• But, when at a distance, there is very little
retinal disparity.
• 2. Distance perception
• a. Monocular Cues
Cues for distance that require one eye.
Example from video.
Judging Distance
Which is closer, the man
or the house?
How can you tell?
-- Interposition
-- Relative size
-- Relative height
-- Linear perspective
-- Relative Clarity
• Linear Perspective
D. DEPTH OR DISTANCE
PERCEPTION
• 3. Nature or nurture?
– When would ability to perceive depth be
important in terms of development?
– Gibson & Walk (1960):
• “Visual Cliff” Experiments
– But, is evidence for nurture also.
• “Use it or lose it”
E. MOTION PERCEPTION
• Another possible innate ability.
• Speculated to have evolved more for survival
than other types of perception. Why?
• Brain makes sense of cues:
– Shrinking objects are retreating.
– Enlarging objects are approaching.
Perceptual Constancy
• Perceptual constancy:
We perceive objects as unchanging even
though the stimuli we receive about those
objects change.
– Importance of experience and expectations?
– babies vs. Pygmies
• Connecting the cues....
–
–
–
–
Distance
Size
Motion
Perceptual Constancy
• Insert slide of Muller-Lyers Illusion
INTERPRETATION IN
PERCEPTION
• Folk, croak, soak...
• 1. Perceptual Set:
A mental predisposition to perceive one
thing and not another.
- Power of our expectations, predisposition –
particularly when interpreting ambiguous
stimuli.
• 2. Review – importance of expectations
– Efficiency
– Can not resist imposing patterns on unpatterned
stimuli (“gestalt”).
– When we see a pattern, difficult to see a
different pattern.
– Even if we formed an incorrect image, difficult
to form a correct one.
• 3. Where do our expectations (schemas)
come from?
– a. Experience
– b. Culture
• Vulnerability to illusions
G. INTERPRETATION AND
PERCEPTION
c. Context
- Context Effects: We often discern the
meaning of something by using the context
in which it is placed.
- rat/man study
- Kulechov effect
Importance of EXPECTATIONS
G. Interpretation in Perception
• How adaptive is our ability to interpret and
organize stimuli into perceptions?
• 4. Perceptual Adaptation:
In vision, the ability to adjust to an artificially
displaced or even inverted visual field.
Conclusions
• Perception: The top-down part of understanding
environment and processing information. Brain
interprets and organizes information.
– Amazing feats of grouping stimuli & using cues.
• But that can also cause illusions...
– Individual differences based on experience and
expectations.
• All of these rely on taking in physical energy from
environment – sensations.
• Assumption: our experiences are tied to actual,
physical events occurring in environment.... see text
H. Perception without Sensation?
•
•
•
•
•
ESP -Extrasensory perception:
Perception without sensory input.
Types of ESP:
Telepathy, Clairvoyance, Precognition
More than ½ Americans believe in some type of
ESP.
• Parapsychologists:
• Psychologists who study psychic phenomena
through case studies and experiments.
H. Perception without Sensation?
• Rhine’s Research
• Conclusion about ESP:
• No sound evidence for para-psychological
phenomena
• No single individual who can demonstrate
psychic powers to independent investigators
•
Impossible Figures
• Example:
• Cocktail Party Effect:
The ability to selectively attend to one voice
among many.